Touch devices or touchscreens have been commonly used in electronic devices such as smart phones, personal computers and game consoles. Some touch devices not only provide a user friendly interface and bring users convenience, but also work in conjunction with a fingerprint sensor for the purpose of data security. For example, the fingerprint sensor can determine whether a user is authorized to use the electronic device by verifying the user's identity in the form of fingerprint. Therefore, touch sensitivity has been the subject of interest in developing advanced touch devices.